Methods and apparatus for efficient IP multicasting in a content-based network

ABSTRACT

Methods and apparatus for assigning physical channels in a content-based network. In an exemplary embodiment, the network comprises a cable television network having a plurality of cable modems, and the physical channels are assigned to the cable modems based at least in part on any multicast transmissions that may exist on the system. When two cable modems are receiving the same multicast transmission, the invention causes tuning of one or more of the cable modems to the same physical channel in order to limit the total number multicast transmissions on the network. Multicast transmissions typically comprise video or audio information, but other types of information may also be multicast according to the invention. In another embodiment, a multicast transmission list (containing a list of multicast transmissions and the corresponding physical channels) is sent to the set of cable modems. This list is used by the modems (or associated CPE) to manage channel allocation and tuning.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to the field of network contentdelivery and bandwidth utilization. More particularly, the presentinvention is directed to efficient multicasting of packetized content ina system incorporating multiple physical channels.

2. Description of Related Technology

Modern cable networks deliver both audio and video programming as wellas Internet access. These services are typically provided via a set ofradio frequency channels transmitted through coaxial cable to thesubscriber's premises. The use of fiber optical cable is also known, andoften both are incorporated in the cable network (Hybrid FiberCoaxial—“HFC”), however the dominant form of the delivery into the home(the last mile) remains the coaxial cable.

To receive the various services provided by the cable network thecustomer is often provided with, or required to obtain, customerpremises equipment (CPE). For video and audio programming the CPE istypically referred to as a “set top box” or STB The set top boxtraditionally sat on top of, or in proximity to, the television set,hence the name. For Internet services, the CPE is typically a cablemodem (CM). The cable modem modulates and demodulates the RF signalsexchanged with the cable network.

Both the cable modem and the set top box receive the set of RF channelsdelivered over the coaxial cable network. This set of RF channelstypically comprise a subset of RF channels dedicated to the transmissionof audio and video information, and a subset of RF channels dedicated tothe delivery of Internet or other data services.

For the delivery of Internet service, the cable modem is tuned to one ofthe RF channels dedicated to providing the Internet service. The cablemodem processes the signals on the RF channel, and forwards the traffic(e.g., Internet protocol or IP packets) to the requesting device ornetwork on the customer premises, as well as allowing packets to be sentupstream from the consumer's premises.

Different groups of cable modems are typically assigned to different RFchannels in order to distribute the traffic more evenly, or achieveother operational goals. In general, assigning different RF channels todifferent modems is an efficient method of distributing traffic acrossthe network.

However, as a DOCSIS cable modem (pre-DOCSIS 3.0), is typically limitedto a theoretical maximum of approximately 40 Mbps of data throughput inthe downstream direction (i.e., from head-end or hub to CPE), the numberof video programs that can be broadcast to a given CPE device connectedto that CM is limited. For example, if a video program consumes 1.5Mbps, then at most, 26 programs 1.5 Mbps×26=39 Mbps) could be receivedat any one time, ignoring for present purposes any overhead associatedwith packet headers, etc. As this 40 Mbps is the limit not only for thesingle modem, but for all modems sharing the same DOCSIS downstream porton a typical CM termination system (CMTS), the number of simultaneousvideo programs broadcast to a given neighborhood served by one CMTS portwould be limited to 26 programs. Given that a typical modern cable videochannel lineup consists of hundreds of different channels, and that highdefinition (HD) content consumes more than 1.5 Mbps, the entire channellineup cannot be replicated on a single DOCSIS 2.0 downstream channel,given currently acceptable video encoding bitrates. Even a hypotheticalfuture cable modem capable of 100 Mbps could not support such abroadcast.

Alternatively, multiple DOCSIS downstream channels could be utilized inorder to transmit all of the aforementioned channels simultaneously.Given a theoretical 200 channel lineup where each video channel isencoded at 1.5 Mbps, and each DOCSIS channel carries 26 programs, then 8DOCSIS downstream channels (8 channels×26 programs/channel=208 programs)would be needed to replicate the video broadcasts over DOCSIS. As aDOCSIS 2.0 CM is only capable of tuning to a single DOCSIS downstreamchannel at any one time, and assuming that there would be multiple userdevices (e.g., TV sets) in use simultaneously in a single premisesserved by a single CM, it is likely that all desired programming forthat premises would not be residing on a single DOCSIS downstreamchannel. Hence, the premises could not receive all of the desiredprograms simultaneously.

Multicast Traffic

More recently, networks have incorporated the use of multicast Internettraffic or multicast Internet Protocol (IP) transmissions. MulticastInternet traffic is traffic directed from one point to many, which isuseful for broadcast type services such as video or audio streaming.

In the day-to-day operation of a cable network, it is often the casethat two cable modems will receive the same multicast transmission. Insome instances, the two cable modems will be assigned to receiveInternet traffic on two different RF channels. In that case, both RFchannels will have to transmit the same multicast transmission.

The traditional video content described above is typically MPEG-basedvideo. Video transported to PCs (or IP-based devices such as STBs) overa DOCSIS network is typically MPEG (or another video codec)-over-IP overMPEG. That is, the higher layer MPEG- or other encoded content isencapsulated using an IP protocol, which then utilizes an MPEGpacketization for delivery over the RF channels used by a DOCSIS devicesuch as the aforementioned cable modem. If the multicast comprises sucha video or other sizable transmission, the amount of network bandwidthconsumed may be substantial. This “wasted” bandwidth reduces the overallefficiency of the cable network.

A variety of different approaches to unicast and multicast packet datadelivery over networks, including content-based (e.g., cable) networks,are present in the prior art. For example, U.S. Pat. No. 6,181,697 toNurenberg, et al. and issued on Jan. 30, 2001 entitled “Method for aunicast endpoint client to access a multicast internet protocol (IP)session and to serve as a redistributor of such session” discloses aendpoint client on an IP Unicast network that is provided access to aMulticast session on an IP Multicast network through a Multicast-Unicastgateway server (MUS) which is enabled to re-Multicast that session toother endpoint clients on the network to which it is connected or toendpoint clients on any Multicast-capable sub-network to which it isdirectly connected. To act as a re-Multicaster, the endpoint clientreceiving Unicast-addressed packets from the session from the MUS,re-translates these Unicast-addressed packets to Multicast-addressedpackets by translating the Unicast address in the distribution field ofeach packet's header into a Multicast address and overwriting theUnicast address in each header with the Multicast address. When anendpoint client on the same or connected sub-network as there-Multicaster desires to join a session that is being re-Multicast, itneeds only connect to that Multicast address. A endpoint client on aUnicast network can elect to be a re-Multicaster of packets from asession as long as that same session is not being re-Multicast byanother endpoint client on any sub-network on which the electingre-Multicaster is connected or a Multicast router is not forwardingpackets from the session onto the sub-network.

U.S. Pat. No. 6,259,701 to Shur, et al. issued Jul. 10, 2001 andentitled “Method and system for a unicast endpoint client to access amulticast internet protocol (IP) session” discloses unicast endpointclients on an IP Unicast network which are provided access to Multicastsessions on an IP Multicast network through a Multicast-Unicast gatewayserver. The server obtains information about sessions on the Multicastnetwork and makes such information available to a Unicast client on theUnicast network upon request by the client. Upon being presented with alist describing the subject matter of each session, the user at theUnicast client selects the session to which he or she wants to join,which causes the Multicast-Unicast server to join the appropriatesession on behalf of the requesting client for each media type in whichthe joining client wants to be a participant. The server then sets abidirectional Unicast User Datagram Protocol (UDP) stream between itselfand the client. All packets then received by the server from the Unicastclient are address-translated to the appropriate Multicast sessionaddress. In addition, all packets received by the server on theMulticast session address are address-translated and sent to the Unicastclient. The Unicast client is then able to participate in the Multicastsession as both a sender and a receiver of packets to and from otherUnicast and Multicast clients which are active during the session.Further, the Unicast client is capable of creating a new session,recording a session in the network for later retrieval and playback, andcreating and accessing low bandwidth versions of existing sessions.

U.S. Pat. Nos. 6,925,257 and 6,519,062 to Yoo both entitled “Ultra-lowlatency multi-protocol optical routers for the next generation internet”disclose an ultra-low latency optical router with a peta-bit-per-secondtotal aggregate switching bandwidth, that will scale to a totalconnectivity of 1000 by 1000, and beyond by modular upgrades. The unitserves as an engine to other optical routers that can function in thecontext of circuit-switching, flow-switching, burst-switching, andpacket-switching. The unit uses advanced wavelength conversiontechnology to achieve three methods of contention resolution in therouter: deflection in wavelength, deflection in space, and buffering intime, and that interfaces a local network to the Supernet.

United States Patent Publication No. 20010004768 to Hodge, et al.published Jun. 21, 2001 entitled “Highly integrated computer controlleddigital head end” discloses a highly integrated computer controlleddigital headend configured to process a plurality of digital video, aplurality of digital data, a plurality of voice information, and aplurality of upstream communications. The digital headend includes atleast one smart network interface module operatively coupled to a sharedbus, a downstream module and an upstream module. Preferably, the smartnetwork interface module is configured to receive, transfer and bufferthe plurality of digital video, the plurality of digital data, theplurality of voice information and the plurality of upstreamcommunications. The shared bus is operatively coupled to the at leastone smart network interface module. The shared bus is configured totransport the digital video, the plurality of digital data, theplurality of voice information, and the plurality of upstreamcommunications. The downstream module is operatively coupled to theshared bus. The downstream module is configured to transmit theplurality of digital video, the plurality of digital data and theplurality of voice information.

United States Patent Publication No. 20010005908 to Hodge, et al.published Jun. 28, 2001 and entitled “Method for buffering video, dataand voice signals using a common shared bus” discloses a method forcombining a plurality of digital video signals, a plurality of digitaldata signals, a plurality of voice signals, and a plurality of upstreamcommunications within a digital broadband headend. This digitalbroadband headend uses a common shared bus to optimize the resourcesused on a digital headend. More particularly, the method comprisesproviding a video interface for receiving the plurality of digital videosignal, providing a data interface for receiving the plurality ofdigital data signals, and providing a voice interface for receiving theplurality of voice signals. The method then proceeds to process theplurality of digital video signals, digital data signals and voicesignals. After this processing is completed by the digital headend, theplurality of digital video signals is communicated to at least one smartnetwork interface module which is configured to buffer the plurality ofdigital video signals.

United States Patent Publication No. 20020056125 to Hodge, et al.published on May 9, 2002 and entitled “Multi-tier buffering system andmethod which combines video, data, and voice packets” discloses adigital headend system for communicating a plurality of video packets,data packets, voice packets, and control packets. The system includes abuffering module, a re-packetization module, and a synchronizationmodule. The buffering module receives the plurality of video packets,data packets, voice packets, control packets or any combination ofpackets. Preferably, the buffering module generates a destinationaddress which identifies a particular re-packetization module. Theidentified re-packetization module is in communication with thebuffering module. The first re-packetization module combines theplurality of video packets, data packets, voice packets, control packetsor any combination thereof. The synchronizing module receives there-packetization output and generates a synchronous output stream havingthe plurality of video packets, data packets, voice packets, controlpackets or any combination thereof. Preferably, the synchronous outputstream is comprised of MPEG transport packets. The present inventionalso provides a method for communicating the plurality of video packet,data packet, voice packet, control packets, or any combination thereof.

United States Patent Publication No. 20040045032 to Cummings, et al.published Mar. 4, 2004 and entitled “MiniMAC implementation of adistributed cable modem termination system (CMTS) architecture”discloses a miniMAC implementation of a distributed CMTS in a hybridfiber/coaxial (HFC) plant. The distributed CMTS comprises at least onenetwork layer, at least one media access layer, and one or more physicallayers. The at least one media access layer includes one or more miniMAClayers. The one or more miniMAC layers are remotely located from aremaining part of the at least one media access layer. The at least onenetwork layer, the remaining part of the at least one media accesslayer, the one or more miniMAC layers, and the one or more physicallayers each function as separate modules, enabling each layer to be inseparate component locations of the HFC plant, yet having the at leastone network layer connected to the remaining part of the at least onemedia access layer, the at least one media access layer connected toeach of the one or more miniMAC layers, and each of the one or morephysical layers connected to each of the one or more miniMAC layers. Theone or more miniMAC layers are located in close proximity to the one ormore physical layers in the HFC plant. The one or more miniMAC layersconvert digital bit streams into packets and maintain timing constraintsbetween the one or more miniMAC layers and the one or more physicallayers.

United States Patent Publication No. 20040045037 to Cummings, et al. andpublished Mar. 4, 2004 entitled “Distributed cable modem terminationsystem (CMTS) architecture implementing a media access control chip”discloses a distributed cable modem termination system (CMTS) in ahybrid fiber/coaxial (HFC) plant. The distributed CMTS comprises anetwork layer, at least one media access control layer, and at least onephysical layer. The media access control layer implements a media accesscontrol chip. The media access control chip interfaces with the physicallayer to provide timing to maintain components within the physicallayer. At least one physical layer is connected to a respective at leastone media access control layer. The network layer, media access controllayer, and physical layer each function as separate modules. The mediaaccess control chip does not require packet level media access controlfunctions to be implemented in the same physical location. See alsoUnited States Patent Publication No. 20040045035 to Cummings, et al.published Mar. 4, 2004 entitled “Distributed cable modem terminationsystem (CMTS) architecture,” and

United States Patent Publication No. 20050002331 to Nolle, et al.published Jan. 6, 2005 and entitled “Predictive upstream load balancing”discloses the static balancing of cable modems across upstream channelswhich are made based on the channel's current bandwidth demand comparedto a first and/or second CAC threshold level. If both threshold levelsare exceeded, the modem is assigned to the channel having the lowestbandwidth demand. After registration, predictive balancing modemsaccording to whether an MTA is part of a given modem avoidsconcentration of modems having MTAs on certain channels while otherchannels serve only modems without MTAs. Modems are also predictivelybalanced according to whether they have associated a DSA_use_historyprofile. Modems associated with certain subscribers may be balancedaccording to the time of day balancing is occurring based on theprofile. Thus, light user's during working hours may be balanced asheavy user's at night if they typically download video content or useVoIP features during the evening.

“Switched” Architectures

One emerging technology useful for efficiently delivering video andother content to network subscribers comprises so-called “switched” or“broadcast switched” architectures. These systems make use of the factthat while a given number of channels of programming or content must bemade available to a given pool of subscribers, not all of these channels(and in fact, not even most of these channels) are required to actuallybe delivered to subscribers at any given time. Rather, only a fractionof these channels are requested. Hence, the use of “intelligent” andprompt switching of these channels can obviate the need to deliver allof the channels simultaneously; only those channels actually beingviewed or requested are switched onto the QAMs for delivery to theappropriate subscribers.

However, such switched functionality has heretofore only been applied tomore traditional broadcast video as opposed to packetized IP mediatraffic, such as the multicast traffic previously described (whichincludes so-called “IP-TV”).

Despite the foregoing wide variety of packetized media processing anddelivery techniques evidenced in the prior art, there is still a salientneed for improved apparatus and methods for distributing multicast IP orother packetized content over a content-based (e.g., cable) network inan efficient and flexible manner. Such apparatus and methods wouldideally leverage existing infrastructure and require little in the wayof network modification in order to be implemented, yet provide networkoperators with the ability to deliver multicast traffic (includingrelatively high bandwidth video content) to multiple network userswithout monopolizing numerous downstream channels.

The improved apparatus and methods would also ideally be adaptable tovarying types of network architectures, including those of the digital“switched broadcast” variety, and leverage the inherent attributes ofthese networks to provide even more efficient delivery of packetservices.

SUMMARY OF THE INVENTION

The present invention satisfies the foregoing needs by providing, interalia, efficient multicasting in a system incorporating multiple physicalchannels.

In accordance with a first aspect of the invention, a method ofproviding a plurality of content channels to network subscribers isdisclosed. In one embodiment, the network comprises a broadcast-switchedarchitecture (BSA) cable network having at least one cable modemtermination system (CMTS) and a plurality of cable modems in signalcommunication therewith, and the method comprises: transmitting firstpacketized content over a first channel to at least a first of saidmodems; transmitting second packetized content over a second channel toat least a second of said modems; and selectively switching said secondmodem to said first channel so that said first and second modems receivesaid first and second packetized content in a substantially multicastfashion from the same physical channel. The first and second channelscomprise a portion of the plurality of content channels, at least aportion of said plurality of channels being switched for delivery to CPElocated proximate to respective ones of said plurality of cable modems.

In a second aspect of the invention a system for performing multicastingover a cable network is disclosed. In one embodiment, the systemcomprises: a plurality of cable modems; a cable modem termination systemin data communication with said plurality of cable modems; and acontroller adapted to track the state of multicast transmissions to saidplurality of cable modems, detect that a cable modem assigned to a firstphysical channel selects a combination multicast transmissions availableon a second physical channel, and cause said cable modem to switch froma first channel to said second channel.

In a third aspect of the invention, a method of operating a network isdisclosed. In one embodiment, the network comprises a cable televisionnetwork that comprises a plurality of cable modems, a modem terminationsystem and a plurality of physical channels allowing communicationbetween said plurality of cable modems and said cable modem terminationsystem, and the method of operating comprises: monitoring a first cablemodem receiving a first multicast transmission on a first physicalchannel; detecting a second cable modem assigned to a second physicalchannel receiving said first multicast transmission; and causing saidsecond cable modem to switch to said first physical channel.

In a fourth aspect of the invention, a method of operating a cable modemin a cable network is disclosed. In one embodiment, the methodcomprises: receiving IP packets on a first physical channel; generatinga request to receive a multicast transmission; receiving informationused as the basis of switching said cable modem to a second physicalchannel; and switching said cable modem to said second physical channel.

In a fifth aspect of the invention, cable modem apparatus adapted toprocess network traffic is disclosed. In one embodiment, the apparatuscomprises: a digital signal processing unit capable of processing datafrom a first physical channel; and a control unit configured to generatea request to receive a multicast transmission, to receive a message toswitch from a first physical channel to a second physical channel inresponse to said request, and to configure said digital signalprocessing unit to process said second physical channel.

In a sixth aspect of the invention, apparatus adapted to controlmulticasting within a cable network is disclosed. In one embodiment, thecable network includes a plurality of cable modems, and the apparatuscomprises: a cable modem termination system communicating with saidplurality of cable modems; and a controller adapted to track the stateof multicast transmissions to said cable modems, said controller beingable to detect that a cable modem assigned to a first physical channelof said network selects a multicast transmission available on a secondphysical channel, and instruct said cable modem to switch from saidfirst channel to said second channel.

In a seventh aspect of the invention, a method of operating a cablenetwork to efficiently deliver multicast packetized transmissions isdisclosed. In one embodiment, the cable network comprises a hub, aplurality of cable modems, and a set of physical channels providingcommunication between said hub to said cable modems, and the methodcomprises: transmitting a multicast transmission list message from saidhub to at least a portion of said cable modems, said message listing aset of multicast transmissions and at least one corresponding physicalchannel on which each multicast transmission is being transmitted;receiving a request to receive a first multicast transmission from saidset of multicast transmissions; and configuring at least one of saidcable modems to process a physical channel associated with said firstmulticast transmission based at least in part on said multicasttransmission list message.

In an eighth aspect of the invention, a method of conserving bandwidthduring delivery of packet services in a network is disclosed. In oneembodiment, the network comprises a “switched” content-based networkhaving a node and a plurality of subscriber devices adapted to receivepacket service from said node, and the method comprises: selectivelyswitching one or more of a plurality of downstream packet channels onlywhen they are required by one or more users being serviced by said node;and selectively switching one or more of said subscriber devices to apacket service channels of said node so as to deliver a common multicasttransmission to two or more of said devices using said packet servicechannel, said selective switching of said one or more devices obviatingthe need to replicate said multicast transmission on a second packetservice channel.

In a ninth aspect of the invention, consumer premises equipment (CPE)adapted for use in a network is disclosed. In one embodiment, the CPE isadapted to selectively retune itself to at least one of a plurality ofphysical channels based at least in part on (i) a downstreamcommunication received by said CPE that maps at least one multicasttransmission to at least one physical channel, and (ii) a communicationreceived from a client device in communication with said CPE requestingdelivery of said at least one multicast transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram illustrating an exemplary HFC cablenetwork configuration useful with the present invention.

FIG. 1 a is a functional block diagram illustrating one exemplary HFCcable network head-end configuration useful with the present invention.

FIG. 1 b is a functional block diagram illustrating one exemplary localservice node configuration useful with the present invention.

FIG. 1 c is a functional block diagram illustrating one exemplarybroadcast switched architecture (BSA) network useful with the presentinvention.

FIG. 2 is a block diagram of an exemplary hub and associated cablemodems configured in accordance with one embodiment of the invention.

FIG. 3 is a logical flow chart illustrating a first exemplary embodimentof the method of channel switching in accordance with the invention.

FIG. 4 a logical flow chart illustrating a second exemplary embodimentof the method of channel switching in accordance with the invention.

FIG. 4 a is a graphical representation of one exemplary format for thetable mapping message (TMM) of the invention.

FIG. 5 is a logical flow chart illustrating a third exemplary embodimentof the method of channel switching in accordance with the invention.

FIG. 6 is a logical flow chart illustrating a fourth exemplaryembodiment of the method of channel switching in accordance with theinvention.

FIG. 7 is a logical flow chart illustrating a fifth exemplary embodimentof the method of channel switching in accordance with the invention.

FIG. 8 is a functional block diagram illustrating an exemplary networkhub controller device according to the invention.

FIG. 9 is a functional block diagram illustrating an exemplary CPEdevice according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to the drawings wherein like numerals refer tolike parts throughout.

As used herein, the terms “user channel” and “program channel” are allgenerally synonymous with the concept of a perceived stream ofinformation. For example, a program/user channel might comprise “Channel3” which carries the content of a given network (e.g., NBC). This is tobe distinguished from a physical channel, which is used to physicallycarry and distribute the content, which may for example comprise one ormore QAMs within a given portion of the RF spectrum of a cable system.

As used herein, the term “QAM” refers to modulation schemes used forsending signals over cable networks. Such modulation scheme might useany constellation level (e.g. QPSK, QAM-16, QAM-64, QAM-256 etc.)depending on details of a cable network. A QAM may also refer to aphysical channel modulated according to said schemes.

As used herein, the term “Service Group” refers to either a group ofservice users (e.g. subscribers) or the resources shared by them in theform of entire cable RF signal, only the RF channels used to receive theservice or otherwise treated as a single logical unit by the network forresource assignment.

As used herein, the term “DOCSIS” refers to any of the existing orplanned variants of the Data Over Cable Services InterfaceSpecification, including for example DOCSIS versions 1.0, 1.1, 2.0 and3.0. DOCSIS (version 1.0) is a standard and protocol for internet accessusing a “digital” cable network. DOCSIS 1.1 is interoperable with DOCSIS1.0, and has data rate and latency guarantees (VoIP), as well asimproved security compared to DOCSIS 1.0. DOCSIS 2.0 is interoperablewith 1.0 and 1.1, yet provides a wider upstream band (6.4 MHz), as wellas new modulation formats including TDMA and CDMA. It also providessymmetric services (30 Mbps upstream).

As used herein, the terms “MSO” or “multiple systems operator” refer toa cable, satellite, or terrestrial network provider havinginfrastructure required to deliver services including programming anddata over those mediums.

As used herein, the terms “network” and “bearer network” refer generallyto any type of telecommunications or data network including, withoutlimitation, hybrid fiber coax (HFC) networks, satellite networks, telconetworks, and data networks (including MANs, WANs, LANs, WLANs,internets, and intranets). Such networks or portions thereof may utilizeany one or more different topologies (e.g., ring, bus, star, loop,etc.), transmission media (e.g., wired/RF cable, RF wireless, millimeterwave, optical, etc.) and/or communications or networking protocols(e.g., SONET, DOCSIS, IEEE Std. 802.3, ATM, X.25, Frame Relay, 3GPP,3GPP2, WAP, SIP, UDP, FTP, RTP/RTCP, H.323, etc.).

As used herein, the terms “Internet” and “internet” are usedinterchangeably to refer to inter-networks including, withoutlimitation, the Internet.

As used herein, the term “head-end” refers generally to a networkedsystem controlled by an operator (e.g., an MSO) that distributesprogramming to MSO clientele using client devices. Such programming mayinclude literally any information source/receiver including, inter alia,free-to-air TV channels, pay TV channels, interactive TV, and theInternet. DSTBs may literally take on any configuration, and can beretail devices meaning that consumers may or may not obtain their DSTBsfrom the MSO exclusively. Accordingly, it is anticipated that MSOnetworks may have client devices from multiple vendors, and these clientdevices will have widely varying hardware capabilities. Multipleregional head-ends may be in the same or different cities.

As used herein, the terms “client device” and “end user device” include,but are not limited to, set-top boxes (e.g., DSTBs), personal computers(PCs) and minicomputers, whether desktop, laptop, or otherwise, andmobile devices such as handheld computers, PDAs, and smartphones.

Similarly, the terms “Customer Premises Equipment (CPE)” and “hostdevice” refer to any type of electronic equipment located within acustomer's or user's premises and connected to a network. The term “hostdevice” refers generally to a terminal device that has access to digitaltelevision content via a satellite, cable, or terrestrial network. Thehost device functionality may be integrated into a digital television(DTV) set. The term “customer premises equipment” (CPE) includes suchelectronic equipment such as set-top boxes (e.g., DSTBs), televisions,cable modems (CMs), whether stand-alone or integrated with otherdevices, Digital Video Recorders (DVR), gateway storage devices(Furnace), and ITV Personal Computers.

As used herein, the term “network agent” refers to any network entity(whether software, firmware, and/or hardware based) adapted to performone or more specific purposes. For example, a network agent may comprisea computer program running in server belonging to a network operator,which is in communication with one or more processes on a CPE or otherdevice.

As used herein, the term “application” refers generally to a unit ofexecutable software that implements a certain functionality or theme.The themes of applications vary broadly across any number of disciplinesand functions (such as on-demand content management, e-commercetransactions, brokerage transactions, home entertainment, calculatoretc.), and one application may have more than one theme. The unit ofexecutable software generally runs in a predetermined environment; forexample, the unit could comprise a downloadable Java Xlet™ that runswithin the JavaTV™ environment.

As used herein, the term “computer program” or “software” is meant toinclude any sequence or human or machine cognizable steps which performa function. Such program may be rendered in virtually any programminglanguage or environment including, for example, C/C++, Fortran, COBOL,PASCAL, assembly language, markup languages (e.g., HTML, SGML, XML,VoXML), and the like, as well as object-oriented environments such asthe Common Object Request Broker Architecture (CORBA), Java™ (includingJ2ME, Java Beans, etc.) and the like.

As used herein, the term “server” refers to any computerized component,system or entity regardless of form which is adapted to provide data,files, applications, content, or other services to one or more otherdevices or entities on a computer network.

OVERVIEW

The present invention provides, inter alia, methods and apparatusdirected to eliminating or reducing wasted bandwidth associated withmulticasting packetized content (including video or another such sizabletransmission), and thereby increasing the overall efficiency of thecontent-based network.

In one exemplary embodiment, the system of the present inventionutilizes a “switched digital” approach to (i) deliver packetized contentonly when requested, and (ii) selectively switch cable modems (CMs) orother such CPE to and from certain downstream channels (e.g., DOCSISQAM-modulated RF channels) based on switching algorithms. Thesealgorithms make use of the fact that in a typical “switched”environment, only a fraction of the available program channels areactually in use; hence, intelligent and timely switching of individualsubscribers (or groups of subscribers) can allow for a great reductionin the number of downstream channels that must be allocated to deliveryof the content.

In the exemplary DOCSIS environment, the subscriber's cable modems areswitched selectively among different downstream QAMs in similar fashionto the switched video previously described, thereby allowing forreduction in the total number of QAMs required to service the DOCSISfunctionality (which may include both traditional IP-based networkservices, as well as high-bandwidth video or “IP TV” content).Advantageously, these cable modems can be rapidly switched with nore-ranging or registration, thereby allowing for a substantiallyseamless and low-overhead switching transient which is transparent tothe user.

The foregoing approach is particularly useful in the content of IP orsimilar “multicast” content that is targeted for multiple subscribers.Under the prior art, multicasting of such content would consumesignificant amounts of bandwidth on the downstream channels, since themulticast content was essentially replicated for each differentsubscriber. In contrast, the improvements provided by the presentinvention allow this multicast content to be delivered to multiplesubscribers by selectively tuning the subscribers to common channelswhere the content is already being delivered to other subscribers,thereby allowing for a 1:N expansion of the content with minimal if anyreplication.

In one exemplary variant of the invention, individual CPE are configuredto perform the switching in a substantially autonomous fashion (e.g.,based on broadcast downstream messages that provide information relatingto the channel mapping of certain packetized content), thereby obviatingany upstream signaling or messages.

The foregoing improvements provided by the invention can also beimplemented in varying types of network architectures, including withoutlimitation traditional cable (HFC) networks, and the more recentbroadcast switched architecture (BSA) type. Minimal modifications tothese networks (and the subscriber's CPE) are advantageously required inorder to implement this functionality. For example, in the case of theBSA network, the DOCSIS switching capability can be readily piggy-backedonto the existing video switching apparatus and algorithms, therebyobviating expensive retrofits and hardware changes.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the apparatus and methods of the presentinvention are now described in detail. While these exemplary embodimentsare described in the context of the aforementioned hybrid fiber coax(HFC) cable architecture having an multiple systems operator (MSO),digital networking capability, and plurality of client devices/CPE, thegeneral principles and advantages of the invention may be extended toother types of networks and architectures where bandwidth conservationis required or desirable, whether broadband, narrowband, wired orwireless, content or data, or otherwise. Hence, the followingdescription is merely exemplary in nature. For example, the inventionmay be practiced over a fiber-to-the-home (FTTH) or fiber-to-the-curb(FTTC) system or over future satellite or millimeter wave-based networkhaving two-way capabilities similar to today's digital cable HFCnetworks.

It will also be appreciated that while described generally in thecontext of a network providing service to a customer or consumer (i.e.,residential) end user domain, the present invention may be readilyadapted to other types of environments including, e.g.,commercial/enterprise, and government/military applications. Myriadother applications are possible.

It is further noted that while described primarily in the context of 6MHz RF channels, the present invention is applicable to literally anyfrequency/bandwidth, such as for example 8 MHz channels. Furthermore, asreferenced above, the invention is in no way limited to traditionalcable system frequencies (i.e., below 1 GHz), and in fact may be usedwith systems that operate above 1 GHz band in center frequency orbandwidth, to include without limitation so-called ultra-widebandsystems.

Also, while described primarily in the context of the well-knownInternet Protocol (described in, inter alia, RFC 791 and 2460), it willbe appreciated that the present invention may utilize other types ofprotocols (and in fact bearer networks to include other internets andintranets) to implement the described functionality.

Network—

FIG. 1 illustrates a typical content-based network configuration withwhich the packet multicasting methodology of the present invention maybe used. The various components of the network 100 include (i) one ormore data and application origination points 102; (ii) one or morecontent sources 103, (iii) one or more application distribution servers104; (iv) one or more VOD servers 105, and (v) consumer premisesequipment (CPE) 106. The distribution server(s) 104, VOD servers 105 andCPE(s) 106 are connected via a bearer (e.g., HFC) network 101. A simplearchitecture comprising one of each of the aforementioned components102, 104, 105, 106 is shown in FIG. 1 for simplicity, although it willbe recognized that comparable architectures with multiple originationpoints, distribution servers, VOD servers, and/or CPE devices (as wellas different network topologies) may be utilized consistent with theinvention. For example, the head-end architecture of FIG. 1 a (describedin greater detail below) may be used.

The data/application origination point 102 comprises any medium thatallows data and/or applications (such as a VOD-based or “Watch TV”application) to be transferred to a distribution server 104. This caninclude for example a third party data source, application vendorwebsite, CD-ROM, external network interface, mass storage device (e.g.,RAID system), etc. Such transference may be automatic, initiated uponthe occurrence of one or more specified events (such as the receipt of arequest packet or ACK), performed manually, or accomplished in anynumber of other modes readily recognized by those of ordinary skill.

The application distribution server 104 comprises a computer systemwhere such applications can enter the network system. Distributionservers are well known in the networking arts, and accordingly notdescribed further herein.

The VOD server 105 comprises a computer system where on-demand contentcan be received from one or more of the aforementioned data sources 102and enter the network system. These servers may generate the contentlocally, or alternatively act as a gateway or intermediary from adistant source.

The CPE 106 includes any equipment in the “customers' premises” (orother locations, whether local or remote to the distribution server 104)that can be accessed by a distribution server 104. Such CPEs 106comprise processors and associated computer memory adapted to store andrun the downloaded or resident application, as well as receive thestreamed in-band content. These may take the form of digital set-topboxes (DSTBs) or the like. The CPE 106 may also comprise a cable modemfor processing Internet or other packetized traffic.

Referring now to FIG. 1 a, one exemplary embodiment of a head-endarchitecture useful with the present invention is described. As shown inFIG. 1 a, the head-end architecture 150 comprises typical head-endcomponents and services including billing module 152, subscribermanagement system (SMS) and CPE configuration management module 154,cable-modem termination system (CMTS) and OOB system 156, as well asLAN(s) 158, 160 placing the various components in data communicationwith one another. It will be appreciated that while a bar or bus LANtopology is illustrated, any number of other arrangements as previouslyreferenced (e.g., ring, star, etc.) may be used consistent with theinvention. It will also be appreciated that the head-end configurationdepicted in FIG. 1 a is high-level, conceptual architecture and thateach MSO may have multiple head-ends deployed using customarchitectures.

The architecture 150 of FIG. 1 a further includes amultiplexer/encrypter/modulator (MEM) 162 coupled to the HFC network 101adapted to “condition” content for transmission over the network. Thedistribution servers 104 are coupled to the LAN 160, which providesaccess to the MEM 162 and network 101 via one or more file servers 170.The VOD servers 105 are coupled to the LAN 160 as well, although otherarchitectures may be employed (such as for example where the VOD serversare associated with a core switching device such as an 802.3z GigabitEthernet device). As previously described, information is carried acrossmultiple channels. Thus, the head-end must be adapted to acquire theinformation for the carried channels from various sources. Typically,the channels being delivered from the head-end 150 to the CPE 106(“downstream”) are multiplexed together in the head-end and sent toneighborhood hubs (FIG. 1 b) via a variety of interposed networkcomponents.

Content (e.g., audio, video, etc.) is provided in each downstream(in-band) channel associated with the relevant service group. Tocommunicate with the head-end or intermediary node (e.g., hub server),the CPE 106 may use the out-of-band (OOB) or DOCSIS channels andassociated protocols. The OCAP 1.0, 2.0 (and subsequent) specificationprovides for exemplary networking protocols both downstream andupstream, although the invention is in no way limited to these exemplaryapproaches.

It will also be recognized that the multiple servers (broadcast, VOD, orotherwise) can be used, and disposed at two or more different locationsif desired, such as being part of different server “farms”. Thesemultiple servers can be used to feed one service group, or alternativelydifferent service groups. In a simple architecture, a single server isused to feed one or more service groups. In another variant, multipleservers located at the same location are used to feed one or moreservice groups. In yet another variant, multiple servers disposed atdifferent location are used to feed one or more service groups.

As shown in FIG. 1 b, the network 101 of FIGS. 1 and 1 a comprises afiber/coax arrangement wherein the output of the MEM 162 of FIG. 1 a istransferred to the optical domain (such as via an optical transceiver177 at the head-end or further downstream). The optical domain signalsare then distributed to a fiber node 178, which further distributes thesignals over a distribution network 180 to a plurality of localservicing nodes 182. This provides an effective 1:N expansion of thenetwork at the local service end.

“Switched” Networks—

FIG. 1 c illustrates an exemplary “switched” network architecture usefulwith the present invention. While a so-called “broadcast switchedarchitecture” or BSA network is illustrated in this exemplaryembodiment, it will be recognized that the present invention is in noway limited to such architectures.

Switching architectures allow improved efficiency of bandwidth use forordinary digital broadcast programs. Ideally, the subscriber will beunaware of any difference between programs delivered using a switchednetwork and ordinary streaming broadcast delivery.

FIG. 1 c shows the implementation details of one exemplary embodiment ofthis broadcast switched network architecture. Specifically, the head-end150 contains switched broadcast control and media path functions 190,192; these element cooperating to control and feed, respectively,downstream or edge switching devices 194 at the hub site which are usedto selectively switch broadcast streams to various service groups. A BSAserver 196 is also disposed at the hub site, and implements functionsrelated to anticipatory switching and bandwidth conservation (inconjunction with a management entity 198 disposed at the head-end). Anoptical transport ring 197 is utilized to distribute the densewave-division multiplexed (DWDM) optical signals to each hub in anefficient fashion.

Co-owned and co-pending U.S. patent application Ser. No. 09/956,688filed Sep. 20, 2001 and entitled “Technique For Effectively ProvidingProgram Material In A Cable Television System”, incorporated herein byreference in its entirety, describes one exemplary broadcast switcheddigital architecture useful with the present invention, although it willbe recognized by those of ordinary skill that other approaches andarchitectures may be substituted.

In addition to “broadcast” content (e.g., video programming), thesystems of FIGS. 1 a-1 c also deliver Internet data services using theInternet protocol (IP), although other protocols and transportmechanisms of the type well known in the digital communication art maybe substituted. As previously described, one exemplary delivery paradigmcomprises delivering MPEG-based video content, with the videotransported to user PCs (or IP-based STBs) over the aforementionedDOCSIS channels comprising MPEG (or other video codec such as H.264 orAVC) over IP over MPEG. That is, the higher layer MPEG- or other encodedcontent is encapsulated using an IP protocol, which then utilizes anMPEG packetization of the type well known in the art for delivery overthe RF channels. In this fashion, a parallel delivery mode to the normalbroadcast delivery exists; i.e., delivery of video content both overtraditional downstream QAMs to the tuner of the user's STB or otherreceiver device for viewing on the television, and also as packetized IPdata over the DOCSIS QAMs to the user's PC or other IP-enabled devicevia the user's cable modem.

Referring again to FIG. 1 c, the IP packets associated with Internetservices are received by edge switch 194, and forwarded to the cablemodem termination system (CMTS) 198. The CMTS examines the packets, andforwards packets intended for the local network to the edge switch 194.Other packets are discarded or routed to another component.

The edge switch 194 forwards the packets receive from the CMTS 198 tothe QAM modulator 189, which transmits the packets on one or morephysical (QAM-modulated RF) channels to the CPEs. The IP packets aretypically transmitted on RF channels that are different that the RFchannels used for the broadcast video and audio programming, althoughthis is not a requirement. The CPE 106 are each configured to monitorthe particular assigned RF channel (such as via a port or socketID/address, or other such mechanism) for IP packets intended for thesubscriber premises/address that they serve.

It will be appreciated that while the exemplary embodiments presentedherein are described in the context of Internet services that includemulticast and unicast data, the present invention is applicable to othertypes of services that include multicast transmission of data deliveredover a network having multiple physical channels or even virtual orlogical channels. For example, switching between various physicalchannels that comprise a virtual channel, can itself be conductedaccording to the “switched” approach of the present invention. As asimple illustration, if a first virtual channel is comprised of physicalchannels (e.g., QAMs) A, B and D, and a second virtual channel iscomprised of QAMs C, E and F, a CM or other CPE can be configured toswitch between the A/B/D and C/E/F virtual channels as if they were asingle QAM.

FIG. 2 is a simplified logical diagram of a cable network that moreclearly illustrates the invention. The hub 200 is coupled to a pluralityof customer premise equipment (CPEs) 106, each via a set of physicalchannels 204. The physical channels are typically 6 MHz radio frequencychannels each centered at different frequencies. The RF channels aretypically carried via coaxial cable to the customer premises, althoughother approaches (such as FTTH) may be utilized.

The use of other types of physical channels is also consistent with theinvention, including light in optical fiber and broadcast RF or lightsignals (wireless). Time division and/or code division channels (or yetother access techniques) may also be used. Additionally, completelyseparate physical media may be used such as multiple fiber optic cablesor multiple coaxial cables linked to the same customer site or CPE 106.Heterogeneous mixes of the foregoing physical and/or logical approachesmay also be employed, as will be appreciated by those of ordinary skill.

In the exemplary embodiment of the invention, the CPE 106 comprise cablemodems, although other devices capable of receiving the transmittedsignals may be used. The subscriber typically will have additionalequipment such as set top boxes (STBs), routers, computers or otherclient devices on the premises that may receive IP traffic via (or evenin tandem with) the cable modem. For example, the end destination of IPmulticast traffic may be a mobile device which is in wirelesscommunication with the CM via a wireless gateway or router (e.g., WiFi,Bluetooth, or PAN) device.

The exemplary hub 200 of FIG. 2 includes an edge switch 210, cable modemtermination switch 212, and IP channel controller 214. IP channelcontrol typically comprises software running on a microprocessor,although other approaches (including hardware and firmware) may beemployed if desired. Software, however, allows for flexiblemodifications and upgrades, such as where operational or business rulesare changed.

While the illustrated embodiment shows an IP channel controller 214within the hub 200, the placement of the IP channel controller 214 atother locations is consistent with other embodiments of the invention.For example, the channel controller 214 may comprise a distributedsystem with a portion located in a hub 200 and a portion located at thehead-end or other network node. However, the hub 200 is a preferredlocation for IP channel controller as it is proximate to the CMTS 212.

The configuration of, and communication between, the various componentsthat make up the exemplary network of FIG. 2 are performed primarilythrough control and/or configuration messages. For example, the IPchannel controller 214 may exchange control messages with the CMTS 212in order to allocate certain IP traffic to certain QAMs, and so forth.The use of such control/configuration messages that are exchangedbetween the various systems as is well known in the art; these messageprotocols are typically present within the system to begin with, andhence provide a ready mechanism for support of the various functions ofthe present invention.

In one variant, the CMTS 212 configures the CPE 106 via one or moreconfiguration messages to receive IP traffic on different physicalchannels 204. For example, the CMTS 212 will configure a first subset ofcable modems which it serves to receive IP traffic on physical channel A(as designated by its Channel ID or similar parameter), and configure asecond subset of cable modems to receive IP traffic on physical channelB. The CMTS then forwards the packets received from an upstream sourceto the corresponding physical channel via, e.g., the edge switch 194.

During operation, the CPE 106 each monitor the assigned physical channel204 for IP traffic intended for the subscriber(s) they service. Thismonitoring is accomplished in one embodiment by processing the IPpackets received over the physical channel, and looking at the IPaddress or other identifier (e.g., socket or port identifier) containedtherein. Packets with an IP address assigned to the relevant customersite are forwarded to the equipment located at that customer site. Othertraffic is ignored. This “packet filtering” function may also beperformed by a router or other such device in communication with the CPE106.

As described above, subsets of CPE 106 can be assigned to differentphysical channels 204. Thus, a first subset of CPE 106 will monitorchannel A, and a second subset of CPE will monitor channel B. Assigningdifferent physical channels 204 to different sets of CPE 106 reduces theprocessing required for any given CPE 106. Specifically, IP packetstransmitted on non-assigned physical or logical channels are neverreceived by the respective CPE 106, and therefore no computing resourcesare consumed examining or processing those packets. Also, the digitalsignal processing required to process a single physical channel is lessthan that required to process multiple physical channels; hence, the CPEor other processing entity can be “thinner” in terms of processing powerand hardware capability.

The IP traffic received by the CPE 106 also includes broadcast andmulticast packets (herein referred to collectively as multicast IPpackets or multicast transmissions). Multicast IP packets are packetsdirected to multiple destinations, which may include multiple CPE 106.Multicast IP packets typically carry video and/or audio information(e.g., program streams) that is likely to be viewed simultaneously bymultiple users, or data information (such as, e.g., streaming stockquotes).

In one embodiment of the invention, the IP channel controller 214monitors the incoming and/or outgoing IP traffic for multicasttransmissions. The IP channel controller 214 tracks the particular CPE106 receiving those multicasts, as well as the physical channels 204 towhich each CPE is assigned. The tracking is typically accomplished bymonitoring messages generated by the CPE, including requests to initiatethe receipt of a multicast transmission; however, other approaches maybe used.

As described in greater detail subsequently herein, if the IP channelcontroller 214 detects that two CPE 106 are receiving the same multicasttransmission, it then determines if those two CPE 106 are receiving themulticast IP traffic on the same physical channel.

If the two CPE 106 are receiving traffic on different physical channels,the IP channel controller 214 will instruct one of the CPE 106 to switchover to the other physical channel 204, thereby placing both CPE on thesame channel. Additionally, the IP channel controller 214 instructs theCMTS 199 to place the corresponding unicast IP traffic destined for thesecond device, and cancel the second multicast transmission ifestablished.

For example, in one configuration, a first CPE 106 is receiving IPtraffic on physical channel (e.g., QAM) A and a second CPE 106 isreceiving IP traffic on a physical channel B. These two CPE 106 may alsobe receiving the same multicast transmission. If so, the IP channelcontroller 204 will switch the second CPE 106 to physical channel A (orvice versa) so that a single multicast transmission may be shared byboth CPEs 106. It will also configure the CMTS 199 to transmit theunicast IP traffic destined for or addressed to the second CPE 106 onphysical channel A, and to cancel the second multicast transmission, ifestablished.

By placing both CPE 106 on the same physical channel, the IP channelcontroller 214 increases the efficiency of the network. In particular,the IP channel controller 214 eliminates the need to place the same IPmulticast transmission on two different physical channels. This reducesthe overall network traffic loading, and therefore increases thecapacity of the network. IP multicasts can be very data intensive,particularly when video multicasts are involved, thus the networksavings can be substantial. The greater the bandwidth consumed by themulticast, the greater the benefits provided by the “leveraging” of thepresent invention.

In one embodiment of the invention, the IP channel controller 214 mayalso assist in load-balancing functions. For example, the controller maydetermine which physical channel is more heavily loaded with IP traffic.It can then selectively switch a given CPE 106 assigned to themore-loaded physical channel to the less-loaded physical channel used byanother CPE 106. In this case, the multicast transmission will beswitched from first channel to the second channel. This assists withbalancing the network load by distributing IP traffic across theavailable QAM pool. However, it will be recognized that in certaincases, it may be desirable to load up a given channel at or near itslimit, such as to permit elimination of lightly loaded DOCSIS QAMs thatcan be replaced with additional downstream content channels (such asduring particularly high peak viewing times).

It will also be recognized that the foregoing functionality may beapplied with more than two channels/CPE. For example, if two CPE 106 arealready receiving a multicast transmission on a first physical channel204, and a third CPE 106 assigned to a different physical channel 204 isdetected receiving the same multicast transmission, the IP channelcontroller will switch the third CPE 106 to the first physical channel.This reduces the number of CPE 106 that are required to switch physicalchannels; i.e., as compared to switching the two commonly tuned CPE tothe channel of the third CPE. Hence, the invention can be configured toanalyze the existing CPE/channel allocation, and determine the mostefficient switching strategy that reduces switching transients (andhence overhead).

In another embodiment of the invention, the IP channel controller 214tracks the state of all multicast programming requested by a set of CPE106 that share a set of physical channels 204. If a first CPE 106 usinga first physical channel 204 selects the same set of multicasttransmissions as a second CPE 106 using a second physical channel 204(as determined by, e.g., an upstream message), the IP channel controllerwill instruct the CMTS to cause the second CPE 106 to switch to thefirst physical channel. The switched CPE can then receive the samemulticasts without transmission of any additional information in thenetwork.

It is noted that the exemplary embodiments of the present inventionprovide two-fold benefits in terms of bandwidth conservation; i.e., (i)the selective switching “on” of the downstream DOCSIS channels only whenthey are required by one or more users being serviced by that node(e.g., hub), and (ii) the “compression” of what would otherwise be twoor more separate multicast streams delivered to two or more cable modemsinto one stream, thereby obviating replication of the multicast content.

In terms of channel allocation and capability, video trials conducted bythe Assignee hereof have demonstrated that given an exemplary channellineup of some 200 video programs and a grouping of householdscontaining approximately 250 set top boxes, a maximum of about 40 videochannels will be simultaneously consumed by CPE distributed among thosehouseholds.

Recall that to replicate 200 video programs over DOCSIS requires 8DOCSIS downstream channels. In order to transmit 40 video channels, only2 DOCSIS downstream channels would be necessary (40 streams at 1.5Mbps=60 Mbps/40 Mbps per DOCSIS downstream=2 downstreams). Thus, for aDOCSIS-based video distribution platform, a better solution is toperform switching of the video over a smaller number of DOCSIS 2.0downstream channels. A DOCSIS 2.0 CM is capable of performing very quickdownstream channel changes (DCC), which allows the CM to switch betweenthe multiple DOCSIS downstream channels on which the video content isbroadcast. It is also advantageously possible to perform thesedownstream channel changes without requiring the CM to re-range andre-register.

In a broadcast switched video environment, the switching controllerreceives requests for video from a video display application (e.g.,running on the subscriber's CPE), determines whether that requestedvideo is already being broadcast to the group of subscribers whichincludes the requester, and determines on which of the available QAMs itshould be broadcast. In the DOCSIS video environment, assuming that allCPE 106 in a given premises share a single CM to access the video, andthat single CM is limited to receiving video on a single DOCSISdownstream at any one time, the channel controller 214 is tasked withkeeping track of all channels currently being watched by each premisesor household and ensuring that all channels for each household areavailable on one of the DOCSIS downstreams. This can lead to some lossof statistical multiplexing gains, as some video programs will have tobe made available on multiple DOCSIS downstreams simultaneously, butthis would only be a temporary condition, and can be managed and alsooffset with other techniques. As homes “tune away” from a given channel,those video programs can be removed by the controller 214 from theappropriate DOCSIS downstream channel.

It will also be recognized that the present invention differs fromconventional “IP-based multicast” of type known in the prior art in thatthe present invention creates CMTS/CM pairing(s) to cause the CM tochange which DOCSIS downstream from which it receives the multicastcontent.

In addition, while a simple prior art multicast rendezvous point simplycreates and destroys tree branches as clients join and leave amulticast, the controller 214 of the present invention must keep thestate of all video programming requested (by household) for each ofthose households that share the pool of DOCSIS downstream channels on aparticular CMTS 199. For example, if a given household is usingdownstream channel B, and then selects the same combination of videoprograms that another household is receiving on channel A, then thefirst household's cable modem will be instructed by the controllingentity (e.g., by the CMTS 199 or controller 214, or the CPE itself viabroadcast status messages as described subsequently herein) to switch tochannel A. For example, in one embodiment, the controller 214 tells theappropriate CMTS 199 via inter-component messaging to instruct theappropriate CM (via a separate downstream message addressed to that CM)to make this channel change.

Methods—

Referring now to FIG. 3, a first exemplary method of operating a networkaccording to one embodiment of the invention is described in detail. Themethod 300 begins at step 302 wherein a first cable modem or other CPEis associated with and receives a first multicast transmission on afirst physical channel. Per step 304, a second cable modem is detectedreceiving (or requesting to receive) the multicast transmission on asecond physical channel.

Per step 306, the second cable modem is instructed to switch to thefirst physical channel. In response, at step 308, the second cable modemswitches to begin processing its own (dedicated or unicast) IP packetsas well as the requested multicast packets on the first physicalchannel. The IP traffic destined for or addressed to the second cablemodem is also switched to the first physical channel in anticipatory orsubstantially contemporaneous fashion, so as to minimize the possibilityof packet loss (and hence the need for subsequent retransmission).

Per step 310, the multicast transmission on the second physical channelis terminated (if in progress), thereby freeing up bandwidth on thesecond physical channel, or allowing for its elimination if no otherbandwidth of that channel is currently being utilized.

FIG. 4 is a flow chart illustrating another exemplary method 400 ofnetwork operation performed in accordance with another embodiment of theinvention. The method 400 begins at step 402, wherein the state of allthe multicast transmissions received by the set of CPEs 106 (e.g., cablemodems or CM equipped DSTBs) that share a CMTS is tracked and updated.This updating may be anecdotal, periodic, or upon the occurrence ofanother event (such as an upstream communication or request from a CPE)

At step 404, a CPE 106 is detected that is receiving, or requesting toreceive, a set of multicast transmissions that is the same as a firstCPE 106, but using a different physical channel. Per step 406, the newCPE is instructed to switch to the (different) physical channel used bythe first CPE 106, and the CMTS 214 is configured to forward all IPtraffic addressed to that CPE (or other entities in its network ifacting in a router or gateway capacity) on the new physical channel. Anymulticast transmissions established on the first physical channel usedby the detected CPE are terminated. The process is then terminated (step408).

In similar fashion to the method 300 of FIG. 3, the method 400 of FIG. 4uses the network bandwidth more efficiently by, inter alia. (i)instructing a CMTS/CM pairing to cause the CM to change which downstream(e.g., DOCSIS) channel it receives content from; and (ii) selectivelyreallocating or tearing down unused channels. In a particular salientaspect, the exemplary methods reduce the number of multicasttransmissions on the network by placing CPEs (e.g., CMs) receiving thesame set of multicast transmissions on the same physical (or virtual)channel.

It will also be recognized that the methods of the present invention maybe used with those described in co-owned and co-pending U.S. applicationSer. No. 11/013,671 entitled “METHOD AND APPARATUS FOR WIDEBANDDISTRIBUTION OF CONTENT” filed Dec. 15, 2004 which is incorporatedherein by reference in its entirety. Specifically, in one embodiment,the aforementioned physical channels or QAMs established between the hub(or head-end or other network agent) and the CPE/CM can comprise awideband multiplex if desired. In this capacity, the virtual channelprovided by wideband multiplex acts essentially as a single QAM (whilealso affording the numerous benefits described in the aforementioneddisclosure, including increased multiplexing efficiency). Variouscombinations and implementations of the invention incorporating widebandcapability will be recognized by those of ordinary skill in the art,provided the present disclosure.

In certain applications, there is also a desire to allow the IP STB/PCto continue to receive video programming even in the event that theDOCSIS upstream channel becomes unavailable or is impaired. Hence, inanother embodiment of the invention, the controller 214 periodicallysends out a table mapping message (TMM) or similar communication to therequesting (e.g., video) application on the end-user device, e.g.,IP-enabled STB or PC, or alternatively to the CPE (i.e., CM) itself.This TMM provides the mapping of video programs to DOCSIS downstreamchannel ID and multicast address. FIG. 4 a illustrates one exemplaryformat for the TMM of the invention. Even if a CPE or associated PC isunable to send a “join” message, it can use the information in the TMMto determine whether a requested video program is currently available onthe DOCSIS downstream channel to which it is currently tuned. The CPE/PCis also configured to indicate the appropriate behavior if a videoprogram is only currently available on another DOCSIS channel. If theupstream DOCSIS channel is unavailable, the CM can be programmed to tuneitself to a different DOCSIS downstream to receive the video programs(whether automatically or according to some other logical controlalgorithm). Likewise, the CM can be programmed to use a different DOCSISupstream for communication.

FIG. 5 is a flow chart illustrating an exemplary method of operationaccording to aforementioned logic. The method 500 begins at step 502,wherein the multicast transmissions to the CPEs associated with aparticular CMTS are tracked along with the physical channels on whichthose multicast transmissions are located. Per step 504, a list of themulticast transmissions and the associated physical channels arebroadcast to the CPE 106 associated with the particular CMTS. Thisprocess is repeated periodically in the illustrated embodiment, but maybe performed according to any other number of schemes including, withoutlimitation, (i) anecdotally (i.e., upon the occurrence of a specificevent or sequence of events), (ii) upon receipt of a request, such as anupstream message from one or more CPE 106, or alternatively anothernetwork agent (e.g., server), or (iii) based on one or more monitoredparameters (e.g., available downstream bandwidth, CM activity level,etc.), and so forth.

By broadcasting a list of multicast transmissions and the associatedphysical channels on the downstream QAMs, this embodiment 500 of themethod allows one or more CPE 106 to switch to a different physicalchannel without sending a message to the hub 200 (although one or moremessages may be sent if desired). For example, when a local request isreceived by a CPE 106 to start viewing a multicast transmissioncontained in the list, that CPE can switch to the corresponding physicalchannel without sending a message to the hub 200. By using the broadcastmessage to determine which physical channel contains the desiredmulticast transmission, the CPE can perform this switch almostinstantaneously (and hence avoiding any perceptible latency by the useror any associated application running on the CPE 106, includingretransmission requests and transmissions for any dropped packets) onits own without having to generate a request to an IP channel controlleror CMTS. This is particularly useful where there is no upstream linkavailable due to outage or other impairment, or upstream bandwidth isotherwise constrained or delayed. It is also advantageously enables theuse of “listen only” devices that may operate or functionally act toreceive data from the network only, or which cannot otherwise meetprotocol, timing, or other requirements for upstream communications.

As previously noted, the CPE may also be programmed to search for or tryother upstream communication channels before invoking the aforementionedmethod. For example, the method of FIG. 5 may be selectively employedonly after it has been determined that no upstream channel is available,thereby obviating the periodic broadcast messages until they arerequired.

FIG. 6 is a flow chart illustrating yet another embodiment of theoperating methodology of the invention. The method 600 of FIG. 6 beginsat step 602, wherein a list of multicast transmissions and theassociated physical channels for those transmissions is received. Thesemessages are typically received by a CPE 106, although other networkentities or agents (whether interposed between the CPE and thetransmitting entity, or otherwise) may be used to receive and, interalia, (i) relay, (ii) store for future transmission, or (iii) processthe messages, and generate a new message or signaling to the CPE overanother channel or modality.

Per step 604, a request to receive a multicast transmission contained inthe list is received. This request is typically received by the CPE 106from another system on the customer premises. For example, a personalcomputer connected to a cable modem (CM) could request to view aparticular webcast. However, the present invention further contemplatesthe use of “IPTV” and similar devices which can themselves generate suchrequest, such as via an application running thereon.

In response to the multicast request, the CPE begins processing thephysical channel associated with the requested multicast transmissionper step 606 based on the information contained in the multicasttransmission list. In some instances, this will require changing thetuning from a first physical channel to a second channel. In othercases, it will involve processing an additional physical channel. Oncethe processing of the physical channel begins, the multicasttransmission can then be forwarded to the requesting system (such as acomputer system) on the customer premises, or even a mobile device incommunication therewith. By changing channels using, e.g., theinformation contained in a broadcast message, the present embodiment ofthe invention allows for multicast transmissions to be received withoutthe use of a return channel. Thus, even if the return channel isimpaired, or a receive-only device is utilized, multicast transmissioncan be received and processed by the CPE or other client device.

FIG. 7 is a flow chart illustrating the operation of a cable modem inaccordance with one embodiment of the invention. The method begins atstep 702 wherein IP packets are received on a first physical channel.

At step 704, the cable modem generates a request to receive a multicasttransmission. At step 706, an instruction to switch to a second physicalchannel is received by the cable modem, such as from the CMTS, head-end,or other network agent. The cable modem then tunes to the secondphysical channel per step 708.

By switching to a second physical channel, the method of FIG. 7 providesfor more efficient use of the spectrum available on the cable network.In particular, when a requested multicast transmission is available onanother physical channel (e.g., QAM), a given cable modem (or modems)can switch to that physical channel, thereby eliminating the need toestablish a second multicast transmission on the network.

It will be recognized that while certain aspects of the invention aredescribed in terms of a specific sequence of steps of a method, thesedescriptions are only illustrative of the broader methods of theinvention, and may be modified as required by the particularapplication. Certain steps may be rendered unnecessary or optional undercertain circumstances. Additionally, certain steps or functionality maybe added to the disclosed embodiments, or the order of performance oftwo or more steps permuted. All such variations are considered to beencompassed within the invention disclosed and claimed herein.

Controller Device—

Referring now to FIG. 8, a first embodiment of the improved network IPcontroller device 214 according to the present invention is described.It will be appreciated that while described in the context of a CMTS 199or centralized switching (e.g., BSA) server 196 as shown in FIG. 1 c,the device may be adapted for use at other locations within the network.Furthermore, as previously noted, the IP controller entity 214 maycomprise a distributed functionality, wherein two or more portions of adistributed application (DA) in communication with one another areutilized.

As shown in FIG. 8, the exemplary device 214 comprises a computerizedsystem 801 including a digital processor(s) 804, RAM 805, mass storagedevice 806, and a plurality of interfaces 807 for connection with othernetwork apparatus such as LANs, CMTS 199, QAM modulators, the localservice node hardware, IP routers and other packet network devices,network management and provisioning systems, local PCs, etc. Othercomponents which may be utilized within the controller apparatus 801(depending on where it is employed and how it is physically implemented)include encryption/decryption, amplifiers, board level electroniccomponents, as well as media processors and other specialized SoC orASIC devices. Support for various processing layers and protocols (e.g.,DOCSIS MAC, 802.3, OOB channels, DHCP, SNMP, UDP, SNMP, H.323/RTP/RTCP,VoIP, SIP, etc.) may also be provided as required.

The controller apparatus 801 of FIG. 8 may take any number of physicalforms, comprising for example one of a plurality of discrete modules orcards within a hub or head-end component of the type well known in theart. The controller may also comprise firmware, either alone or incombination with other hardware/software components such as thosepreviously described. Alternatively, the controller apparatus 801 may bea stand-alone device disposed at the hub, head-end, or other location.Numerous other configurations may be used. It may also be integratedwith other types of components (such as satellite transceivers,encoders/decoders, etc.) and form factors if desired.

It can also be appreciated that the methods of the present invention maybe practiced using any configuration or combination of hardware,firmware, or software, and may be disposed within one or any number ofdifferent physical or logical entities. For example, the IP packetcontroller functionality described above may take the form of one ormore computer programs running on a single device disposed within thenetwork (such as the controller apparatus 801). As yet another example,portions of the functionality may be rendered as a dedicated orapplication specific IC (ASIC) having code running thereon. Myriaddifferent configurations for practicing the controller device of theinvention will be recognized by those of ordinary skill in the networkarts provided the present disclosure.

CPE—

FIG. 9 illustrates a first embodiment of the improved CPE 106 accordingto the present invention. As shown in the simplified diagram of FIG. 9,the CPE 106 generally comprises a DOCSIS-compliant embedded system(e.g., cable modem) 901 having an RF front end 902 (including at leastone tuner and QAM modulator/demodulator/and encryption/decryption) forinterface with the HFC network 101 of FIGS. 1-1 c. The CPE 901 may alsoinclude a digital processor(s) 904, storage device 906, and a pluralityof interfaces 908 (e.g., video/audio interfaces, IEEE-1394 “Firewire”,USB, serial/parallel ports, etc.) for interface with other end-userapparatus such as personal computers, personal electronics, WiFi orother network hubs/routers, etc., depending on its level of desiredcapability. Other components which may be utilized within the device(deleted from FIG. 9 for simplicity) various processing layers (e.g.,DOCSIS MAC or DAVIC OOB channel, MPEG, etc.) as well as media processorsand other specialized SoC or ASIC devices. These additional componentsand functionality are well known to those of ordinary skill in the cablemodem and embedded system fields, and accordingly not described furtherherein.

The exemplary modem device 901 may also further comprise one or moresoftware applications or algorithms adapted to receive upstreamcommunications directed to its MAC or DOCSIS layer to include: (i)physical channel tuning messages issued by the controller 214; (ii)broadcast “list” or mapping messages or TMMs; and (iii) communicationsfrom the connected PC or other IP-enabled device. The CPE 901 may alsointegrate all of these functions into one device (e.g., an integratedDSTB/CM and IP-TV device) if desired. A wireless (e.g., WiFi or PAN)gateway may also be integrated into the CM 901, thereby allowing forwireless communication between the device 901 and a local wireless PC,laptop, or mobile device.

In the case of multicast requests received by the CM 901 from aconnected device (e.g., video application running on the connected PC),the CM 901 can pass on or reissue such upstream requests. The upstreambandwidth consumption by the aforementioned protocol is not significant;the size and frequency of messaging by the CM (even when considered inthe aggregate) is effectively inconsequential, thereby making theprocesses of the present invention substantially transparent in terms ofbandwidth consumption.

It is also noted that in the illustrated embodiment, upstreamcommunication is required for viewers to initiate new multicasts (ordelivery thereof). However, if a multicast is already active, theupstream is not needed; rather the CM can merely wait for a TMM thatlists the channels over which the requested multicast is delivered, andthen tune to one of those channels.

In the case of autonomous or stand-alone switching (i.e., where noupstream channel is available), the CM software is configured to analyzethe TMM or comparable messages to identify common multicast delivery viaa physical channel not presently in use by that CM 901, and cause the CMtuner to tune to the appropriate QAM in order to aggregate delivery ofthe multicast traffic as previously described herein. This evaluationcan be conducted on a periodic, continual, or anecdotal basis. Forexample, the algorithm can be programmed to cause the CM 901 toperiodically evaluate the TMMs (such as upon receipt of each new TMMduring streaming of packetized multicast content) to determine iffurther aggregation by retuning is possible.

Operations/Business Rules Engine—

In another aspect of the invention, the aforementioned controller entity214 (e.g., rendered as one or more computer programs) includes aso-called “rules” engine. This engine comprises, in an exemplaryembodiment, a series of software routines running on the parent computerdevice or other associated hardware/firmware environment adapted tocontrol the operation of the DOCSIS allocation and switching algorithmspreviously described. These rules may also be fully integrated withinthe controller 214 itself, and controlled via e.g., a GUI on a PC. Ineffect, the rules engine comprises a supervisory entity which monitorsand selectively controls, via the controller entity 214, the IP contentswitching and delivery functions at a higher level, so as to implementdesired operational or business rules. The rules engine can beconsidered an overlay of sorts to the controller algorithms previouslydescribed herein with respect to FIGS. 3-7. For example, the controller214 may invoke certain operational protocols or decision processes basedon requests received from the CPE 106, demographic data, geographicdata, etc. However, these processes may not always be compatible withhigher level business or operational goals, such as maximizing profit orsystem reliability. Hence, when imposed, the business/operational rulescan be used to dynamically (or manually) control the operation of thecontroller 214. The rules may be, e.g., operational or business-orientedin nature, and may also be applied selectively in terms of time of day,duration, specific local areas, or even at the individual user level.

For example, one rule implemented by the rules engine may compriseinvoking CPE switching only when it is required; i.e., when bandwidthusage relating to additional DOCSIS QAMs becomes an issue. Similarly, arelated rule might impose a moratorium on establishing new QAMs forDOCSIS use (assuming that all multicast requests can be serviced byexisting QAMs via the switching algorithms previously described) until acertain minimum threshold of available bandwidth is present, therebyavoiding contention for bandwidth resources with other services usingnon-DOCSIS channels.

Another rule might consider the allocation of DOCSIS channels based on amore global or network-wide perspective, and/or based on use or viewingpatterns which are common across the entire network (e.g., certain peakviewing periods for IP-TV or similar services), which would benefit fromincreased multicast switching “compression” or aggregation. Along theselines, a heuristic or metric can be used to measure bandwidthcompression, as shown in Eqn. (1):CR=BW_(u)/BW_(s)  Eqn. (1)

Where:

CR=Compression ratio;

BW_(u)=Uncompressed or unswitched bandwidth; and

BW_(s)=Switched or compressed bandwidth.

Hence, when there is no switching, there is no compression and CR=1.However, when the multicasts (CMs) are switched in order to reduceredundancy, CR increases to a value greater than 1, indicating that somelevel of efficiency improvement exists. Clearly, the larger thebandwidth consumed by one instance of the multicast (“static”bandwidth), and the greater the number of users requiring delivery ofthat multicast, the greater the value of CR (and hence the greater theefficiency benefits realized through such switching). An algorithm toanalyze these inputs (i.e., “static” bandwidth and number of usersrequesting the multicast) can be readily fashioned in order to moreaccurately determine the benefits of CM switching, and any tradeoffswith other parameters (such as loss of statistical pool size).

It will also be appreciated that certain subsets of channels can beconsidered a basis for channel switching decisions. For example, asubset of Y channels out of an available pool of X channels may comprisethe basis for the switching algorithms. This may be driven by, interalia, the desire to maintain certain QAM pool statistics while alsoaffording the benefits of CM switching as previously described.

It will be appreciated that less “binary” approaches than that describedabove can be utilized consistent with the invention. For example, asupervisory process (e.g., algorithm) may comprise a fuzzy logic,Bayesian, or similar approach to classify network allocation ofmulticasts/QAMs according to, for example, the level of aggregation ofthe multicasts. A low level of aggregation would correspond to acomparatively higher degree of multicast replication (and hence higherinefficiency), while a high level of aggregation would correlate to ahighly “switched” state wherein little if any replication of multicastsis used (high efficiency). As previously noted, it may be desirableunder certain circumstances to consider other metrics such asstatistical pool efficiency, and hence the aforementioned fuzzy orcomparable processes may be used in a decision-making algorithm in orderto find an optimal balance between the two or more competing objectives.

Many other approaches and combinations of operational and/or businessrules are envisaged consistent with the invention, as will be recognizedby those of ordinary skill when provided this disclosure.

In another aspect, it will be recognized that the present invention canadvantageously be utilized consistent with the methods and apparatusdescribed in co-owned and co-pending U.S. patent application Ser. No.11/186,452 filed Jul. 20, 2005 and entitled “METHOD AND APPARATUS FORBOUNDARY-BASED NETWORK OPERATION”, which is incorporated herein byreference in its entirety. For example, the “switched” system can beused to perform “backhauls” to the local hub or other network node. Forexample, a business-class circuit backhaul to the local hub isenvisioned, such as for “neighborhood camera” applications. In oneexemplary embodiment, separate analog video feeds from one or morecameras (or other sensors) are generated and backhauled using the localcontent-based network distribution system. Specifically, this backhaul”approach removes the downstream bandwidth limitations under prior artapproaches; rather, the only effective limitations are in the upstreamdirection (since the video or other signals from the cameras/sensors arebeing backhauled to the local hub in the upstream direction). Signalreplication of the type well known in the networking arts is used toefficiently make the backhauled content available immediately fortransmission in the downstream direction. The upstream signals may bereplicated on a node-by-node basis, and every node can have its owncameras/sensors if desired. The backhauled signals can be converted toan IP protocol/encapsulation as previously described (if required), andthen delivered over the DOCSIS QAMs to the user's PC or other IP-enableddevice via the CM. Hence, users can be provided with an IP-TV orcomparable version of the backhauled signals via their CM and PC.

These services can form the basis of a business model within theaforementioned cable system, thereby providing an additional revenuestream obtained largely from under-utilized bandwidth already existingwithin the system by virtue of the broadcast switched architecture(BSA). This adds great flexibility to the network operator, and allowsfor generation of revenue from otherwise unutilized “upstream”bandwidth” that is already available in the extant networkinfrastructure.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the invention. Theforegoing description is of the best mode presently contemplated ofcarrying out the invention. This description is in no way meant to belimiting, but rather should be taken as illustrative of the generalprinciples of the invention. The scope of the invention should bedetermined with reference to the claims.

1. In a broadcast-switched architecture (BSA) cable network having at least one cable modem termination system (CMTS) and a plurality of cable modems in signal communication therewith, a method of providing a plurality of content channels to network subscribers via respective ones of said modems, the method comprising: transmitting first packetized content over a first channel to at least a first of said modems; transmitting said first packetized content over a second channel to at least a second of said modems; and selectively switching said second modem to said first channel so that said first and second modems receive said first packetized content in a substantially multicast fashion from the same physical channel; wherein said first and second channels comprise a portion of the plurality of content channels, at least a portion of said plurality of channels being switched for delivery to CPE located proximate to respective ones of said plurality of cable modems.
 2. The method of claim 1, wherein said act of selectively switching further comprises transmitting second content to said first channel substantially contemporaneous with said act of switching said second modem to said first channel, said second content being uniquely addressed to said second modem.
 3. The method of claim 1, further comprising selectively switching at least one of said plurality of channels on or off based on the existence of one or more requests for delivery of the content carried by said at least one channel.
 4. The method of claim 3, wherein said selective switching of said at least one channel on or off is conducted by the same entity that controls said selective switching of said second modem.
 5. A system for performing multicasting over a cable network, comprising: a plurality of cable modems; a cable modem termination system in data communication with said plurality of cable modems; and a controller adapted to track the state of multicast transmissions to said plurality of cable modems, detect that a cable modem assigned to a first physical channel selects a combination of multicast transmissions available on a second physical channel, and cause said cable modem to switch from a first channel to said second channel.
 6. The system as set forth in claim 5, wherein said first physical channel comprises one of a 6 MHz or 8 MHz radio frequency channel.
 7. The system set forth in claim 5, wherein said cable modems are in signal communication with said cable modem termination system via at least a coaxial cable.
 8. The system set forth in claim 5, wherein said controller is in data or signal communication with to said cable modem termination system.
 9. The system set forth in claim 5, wherein said controller comprises software instructions running on a microprocessor.
 10. The system set forth in claim 5, wherein said network comprises a broadcast switched architecture (BSA) network, and said multicast are delivered in tandem to subscribers along with one or more switched broadcast channels.
 11. In a cable television network that comprises a plurality of cable modems, a modem termination system and a plurality of physical channels allowing communication between said plurality of cable modems and said cable modem termination system, a method of operating comprising: monitoring a first cable modem receiving a first multicast transmission on a first physical channel; detecting a second cable modem assigned to a second physical channel receiving said first multicast transmission; and causing said second cable modem to switch to said first physical channel.
 12. The method of claim 11, further comprising causing said cable modem termination system to transmit multicast packets to said second cable modem using said first physical channel.
 13. The method of claim 11, wherein said first physical channel and said second physical channel comprise frequency divided radio frequency channels.
 14. The method of claim 11, further comprising: determining a first packet load on said first physical channel and a second packet load said second physical channel; switching said first cable modem to said second physical channel if said first packet load meets at least one criterion with respect to said second packet load; and switching said second cable modem to said first physical channel if said first packet load does not meet said at least one criterion with respect to said second packet load.
 15. The method of claim 14, wherein said at least one criterion comprises said first packet load being greater than said second packet load.
 16. The method of claim 11, wherein others of said plurality of physical channels carries video broadcast programming.
 17. The method of claim 11, wherein said network comprises a broadcast switched network, and said switching is accomplished at least in part using a controller that also switches broadcast channels for delivery to subscriber premises.
 18. A method for operating a cable modem in a cable network, the method comprising: receiving IP packets on a first physical channel; generating a request to receive a multicast transmission; receiving information used as the basis of switching said cable modem to a second physical channel; and switching said cable modem to said second physical channel; wherein at least one other cable modem is simultaneously receiving said multicast transmission on said second physical channel.
 19. The method as set forth in claim 18, wherein said first physical channel and said second physical channel comprise radio frequency channels carried on a coaxial cable.
 20. The method as set forth in claim 18, wherein said act of generating is performed in response at least to a request to receive a multicast broadcast generated by another system in data communication with said cable modem.
 21. The method as set forth in claim 18, wherein said act of receiving comprises the steps of: receiving unicast IP packets on said first physical channel; and receiving multicast IP packets on said first physical channel.
 22. The method set forth in claim 21, further comprising demodulating a QAM modulated RF signal as part of said act of receiving.
 23. Cable modem apparatus adapted to process network traffic comprising: a digital signal processing unit capable of processing data from a first physical channel; and a control unit configured to generate a request to receive a multicast transmission, to receive a message to switch from a first physical channel to a second physical channel in response to said request, and to configure said digital signal processing unit to process said second physical channel; wherein said message to switch from said first to said second physical channel is received only after it is determined that said multicast transmission has been previously established on said second physical channel.
 24. The cable modem apparatus as set forth in claim 23, wherein said control unit comprises software and a microprocessor for running said software.
 25. The cable modem apparatus as set forth in claim 24, wherein unicast IP packets and multicast IP packets are received on the same physical channel.
 26. The cable modem apparatus as set forth in claim 23, wherein said first physical channel comprises a radio frequency transmission centered at a first frequency and said second physical channel comprises a radio frequency transmission centered at a second frequency.
 27. Apparatus adapted to control multicasting within a cable network, said cable network including a plurality of cable modems, comprising: a cable modem termination system communicating with said plurality of cable modems; and a controller adapted to track the state of multicast transmissions to said cable modems, said controller being able to detect that a cable modem assigned to a first physical channel of said network selects a multicast transmission available on a second physical channel, and instruct said cable modem to switch from said first channel to said second channel.
 28. The apparatus of claim 27, wherein said apparatus is disposed substantially at the hub of a broadcast switched architecture network, and said controller is adapted to perform both said tracking, detecting and instructing, and control of the switching of other channels, said other channels carrying broadcast video content to a plurality of subscriber CPE.
 29. In a cable network comprising a hub, a plurality of cable modems, and a set of physical channels providing communication between said hub to said cable modems, a method of operating said cable network to efficiently deliver multicast packetized transmissions, comprising: transmitting a multicast transmission list message from said hub to at least a portion of said cable modems, said message listing a set of multicast transmissions and at least one corresponding physical channel on which each multicast transmission is being transmitted; receiving a request to receive a first multicast transmission from said set of multicast transmissions; and configuring at least one of said cable modems to process a physical channel associated with said first multicast transmission based at least in part on said multicast transmission list message.
 30. The method as set forth in claim 29, wherein said request is received by said at least one cable modem from a client device in data communication with said at least one modem.
 31. The method as set forth in claim 30, wherein said physical channel associated with said first multicast transmission is also used by at least another one of said modems to receive said first multicast transmission.
 32. In a switched content-based network having a node and a plurality of subscriber devices adapted to receive packet service from said node, a method of conserving bandwidth during delivery of said packet service, comprising: selectively switching one or more of a plurality of downstream packet channels only when they are required by one or more users being serviced by said node; and selectively switching one or more of said subscriber devices to a packet service channel of said node so as to deliver a common multicast transmission to two or more of said devices using said packet service channel, said selective switching of said one or more devices obviating the need to replicate said multicast transmission on a second packet service channel.
 33. Consumer premises equipment (CPE) adapted to selectively retune itself to at least one of a plurality of physical channels based at least in part on (i) a downstream communication received by said CPE that maps at least one multicast transmission to at least one physical channel, said mapping being based at least in part on a determination that another CPE is simultaneously receiving said multicast transmission on said at least one physical channel, and (ii) a communication received from a client device in communication with said CPE requesting delivery of said at least one multicast transmission.
 34. In a cable network having at least one cable modem termination system (CMTS) and a plurality of client devices in signal communication therewith, a method of providing a plurality of content channels to network subscribers, the method comprising: transmitting content over a first channel to a first cable modem associated with a first client device, said first client device being associated with a first subscriber; transmitting said content over a second channel to a second cable modem associated with a second client device, said second client device being associated with a second subscriber; and selectively switching said second cable modem to said first channel to provide a multicast transmission of said content to said first and second subscribers from said first channel.
 35. The method of claim 34, wherein said cable network comprises a broadcast-switched architecture (B SA) cable network.
 36. The method of claim 34, wherein said act of selectively switching is substantially transparent to said first and second subscribers.
 37. The method of claim 34, wherein said act of selectively switching substantially obviates a necessity to replicate said content for said first and second subscribers.
 38. The method of claim 34, wherein said act of selectively switching is affected by providing downstream messages to said first and second client devices, said messages comprising information relating to mapping of said content on said plurality of channels.
 39. The method of claim 34, wherein said acts of transmitting are performed utilizing at least an Internet Protocol (IP) over QAM (quadrature amplitude modulated) transport.
 40. The method of claim 39, wherein said content channels comprise IP television (IPTV) channels.
 41. The method of claim 34, wherein at least one of said first and second channels comprises a wideband multiplex.
 42. In a switched content-based network having a node and a plurality of subscriber devices adapted to receive packet service from said node, a method of conserving bandwidth during delivery of said packet service, comprising: selectively switching a switching apparatus in said switched content-based network for delivery of said one or more of a plurality of downstream packet channels, said selective switching being based at least in part on the presence or absence of a request for individual ones of said channels from at least one subscriber of said network; and selectively switching one or more of said subscriber devices to a packet service channel of said node so as to deliver a common multicast transmission to two or more of said devices using said packet service channel, said selective switching of said one or more devices obviating the need to replicate said multicast transmission on a second packet service channel.
 43. The method of claim 42, wherein said switching apparatus comprises a broadcast switched architecture (BSA) switch disposed at said node, or a node upstream of said node.
 44. The method of claim 43, wherein said switch is adapted to receive a plurality of channels, yet only selectively deliver a subset of said plurality of channels to said subscriber devices. 